CVD apparatus is conventionally used to form various thin films in a semiconductor integrated circuit. Such CVD apparatus can form thin films such as SiO.sub.2, Si.sub.3 N.sub.4, Si or the like with high purity and high quality. In the reaction process of forming a thin film, a reaction vessel in which semiconductor substrates are arranged can be heated to a high temperature condition of 500.degree.-1000.degree. C. Raw material to be deposited can be supplied to the vessel in the form of gaseous constituents so that gaseous molecules are thermally dissociated and combined in the gas and on the surface of the specimen so as to form a thin film.
For instance, U.S. Pat. No. 4,962,727 ("the '727 patent") discloses a CVD apparatus in which a silicon oxide film is formed. The '727 patent points out, however, that silicon oxide molecules adhere to the inner wall surface of the vessel and that the deposit may peel off and even adhere to a wafer surface, thus causing defects in the SiO.sub.2 film being formed.
A plasma-enhanced CVD apparatus utilizes a plasma reaction to create a reaction similar to that of the above-described CVD apparatus but at a relatively low temperature in order to form a thin film. The plasma CVD apparatus includes a specimen chamber, a gas introducing system, and an exhausting system. For instance, such a plasma-enhanced CVD apparatus is disclosed in U.S. Pat. No. 4,401,054, the disclosure of which is hereby incorporated by reference. Plasma is generated in such an apparatus by a microwave discharge through electron cyclotron resonance (ECR). A specimen table is provided in the specimen chamber, and plasma generated in the plasma formation chamber passes through a plasma extracting orifice so as to form a plasma stream in the specimen chamber. The specimen table may have a cooling mechanism in order to prevent a rise in temperature of the specimen due to the plasma action.
A plasma apparatus using ECR for a CVD apparatus, an etching apparatus, a sputtering apparatus or the like for manufacturing semiconductor components is disclosed in U.S. Pat. No. 4,902,934, the disclosure of which is hereby incorporated by reference. Such a plasma apparatus includes a specimen mount in a reaction chamber with electrostatic chuck means for holding a specimen (such as a silicon wafer) in good thermal contact and in a vertical orientation. The specimen mount can also be provided with cooling and heating means. In general, such reaction chambers can be operated under vacuum conditions, and the plasma generation chamber can be formed by walls which are water cooled.
Electrostatic chucking devices are disclosed in U.S. Pat. Nos. 3,993,509; 4,184,188; and 4,384,918, the disclosures of which are hereby incorporated by reference. With such systems, a specimen or wafer is typically located on a dielectric layer, and the wafer supporting surface of such electrostatic chucking arrangements can be larger or smaller than the specimen or wafer supported thereon.
The background of U.S. Pat. No. 4,709,655 ("the '655 patent") discloses that reaction chambers employed for chemical vapor deposition are generally classified as cold-wall or as hot-wall systems. The '655 patent further discloses that in the cold-wall systems, the substrate (wafer) can be heated by inductive coupling, radiant heating, or direct electrical resistance heating of internal support elements. The '655 patent states that when the wafers are mounted on a susceptible material adapted for heating by RF energy, heat is localized to the immediate semiconductor wafer area so that 1) chemical vapor deposition is limited to the heated areas, and 2) the unheated walls are below CVD temperatures thereby reducing depositions on the walls. In plasma-enhanced CVD reactors, however, deposition of a film will occur even on cold walls since heat in the plasma will cause a reaction no matter what the temperature of the reaction surface.
A problem with plasma-enhanced CVD apparatus is that deposits are formed on the wafer and all other surfaces inside the reaction chamber. The deposited film can crack and flake off, resulting in particles on the wafer. Oxide films have inherent stresses as deposited. The energy in the film increases as the film thickness increases. Differential thermal expansion between the deposited film and base material adds additional stress. Although it is known in the art to dry etch deposition surfaces in a reaction chamber, as disclosed by U.S. Pat. No. 4,910,042, there exists a need in the art for improving integrity and adhesion of deposited films to surfaces in the reaction chamber, especially line-of-sight surfaces and target surfaces. The term "line-of-sight surfaces" as used herein means surfaces from which a straight line can be drawn directly to a specimen mounted in the reaction chamber. The term "target surfaces" as used herein means surfaces surrounding the specimen mounted in the reaction chamber and which are directly contacted by a plasma stream. The term "specimen" as used herein means any semiconductor substrate, such as a wafer of silicon or other material, having a flat or uneven surface onto which a film is formed by a plasma reaction.